Why is my mobile data switching on by itself?

After last update that my phone received, galaxy s4 i9505, the update for KNOX / Kids Mode and also i received the "Smart switch" from wireless to mobile data, i have noticed the following:

if iuse 1-2 hours the wireless at home on the mobile, when i switch it off...automatically my phone will turn on my mobile data connection even tough it was not ON before the wireless. Its draining all my mb from my carrier, its insane. Last nite it was the worse, i stayed like always few hours on wireless, i put it off, went to sleep and in the morning woke up and saw mobile data was turned off....anyone know what is causing this and how i can remedy it?